There are a number of ways:
- If you can get psychotherapy on the NHS, it will be free
- You don't pay if you are privately insured and your insurance covers it.
- Most training institutes and psychotherapist organisations have a system of low-cost psychotherapy provided by specially supervised trainees as part of their training
- There are a number of organisations, mostly charities or non-profits, which provide low-cost or free therapy.
So what's the snag? Why would you ever pay? Unfortunately most of these options have some drawbacks as well as advantages. And insurance only helps if you have the insurance.
Getting therapy on the NHS means you need to fit into the NHS systems. Even if you fulfil their criteria exactly, there often are waiting times. Most of the therapy provided is short-term, and sometimes it is done by people who have much less training than private psychotherapists It may be worth trying it out, and if it works, so much the better. If it doesn't, you may be annoyed and disillusioned, but you are not likely to be worse off. You may also sometimes be pushed to take drugs, or try drugs, before being referred to psychotherapy - so you need to consider how you would deal with that situation. But it definitely works for some and is worth a try. Many people think psychotherapy provision and mental health treatment in the NHS are not of the same quality and reliability as the purely physical / medical parts of the NHS. But some parts of the NHS, and for some problems, are really excellent.
Getting low-cost therapy from a trainee may be another option worth considering. It is not at all a "second-best" solution. Many trainees are on their second or third period of training, and have a lot of experience. They also tend to be keen, are often supervised in much more detail and with a higher frequency than registered practitioners, and they may pay a lot of attention to their work with you, write reports, analyse and re-analyse it, etc. The only thing is that it is hard to know if indeed they are right for you, whether they have previous experience (but you can ask!), and how good they are. At best they are as good as any registered therapist; but the variability of their performance and effectiveness may be a bit bigger than that of more experienced counsellors and therapists.
Charities and non-profits are often staffed at least partly with trainees or people on placement. They also have volunteers who have finished their training, and many will be very experienced, too. Many of these organisations will only offer quite short-term or at least time-limited treatment. But equally, quite a few don't have those restrictions. If you can find your way to one of them, and you qualify for what they offer or specialise in (catchment area, special fields such as refugees, people with combat stress, teenagers, etc.) they can offer very good treatment, and a very good deal financially.
The wider context
Now just stand back and look at the issue of free psychotherapy in a wider context. The NHS, supposedly offering "free" medical care, is not really free. The British population pays for the NHS through their taxes, and a substantial part of your taxes, if you are a tax-payer, goes to the NHS. Psychotherapists also need to live. Unless they are working for the NHS and paid by them, or paid by a charity, or do it themselves as a charitable activity, ultimately therapists must be paid somewhere somehow for the work they do. So the idea of paying for a therapist privately is not at all strange. You also pay (if you can) for a lawyer and for a hairdresser. And exactly if you believe (as I do and many others) that psychotherapy can be very effective and appropriate for a whole range of problems and issues that are neither medical nor to do with health, and do not imply that you are "mad" or have an "illness", it is easy to see that it can be quite all right to pay out of your own pocket for psychotherapy (even if it means giving up on a holiday, or halving your cigarette or alcohol consumption for a period).
In the end, when you have decided that you want to have psychotherapy, you have to choose for yourself what options to explore first. Will you first explore the NHS and other free or low-cost options, or will you straight away try to find a private provider?